Radio frequency identification (RFID) systems allow for the identification of objects at a distance and out of line of sight. They are comprised of transponders called radio frequency (RF) tags and RF interrogators (also called readers). The tags are generally smaller and less expensive than interrogators, and are commonly attached to objects such as product packages in stores. When an interrogator comes within range of an RF tag, it may provide power to the tag via a querying signal, or the RF tag may use stored power from a battery or capacitor to send a radio frequency signal to be read by the RFID interrogator.
RF tags may consist of single integrated circuits, circuits and antennas, or may incorporate more complex capabilities such as computation, data storage, and sensing means. Some categories of RFID tags include the following: passive tags that acquire power via the electromagnetic field emitted by the interrogator, semi-passive tags that respond similarly, but also use on-board stored power for other functions, active tags that use their own stored power to respond to an interrogator's signal, inductively coupled tags that operate at low frequencies and short distances via a coil antenna, single or dipole antenna-equipped tags that operate at higher frequencies and longer distances, read-write tags that can alter data stored upon them, full-duplex or half duplex tags, collision arbitration tags that may be read in groups, or non-collision tags that must be read individually.
RFID systems consist of RFID tags, RFID interrogators and middleware computing devices. Downstream processing of RFID signal information such as EPC numbers, GTINs, or UID numbers usually occurs in two stages. Tag responses are and converted to a standard packet form by the reader and sent to the middleware device. The middleware device is responsible for processing the raw information into a useful form. For instance, a reader may send many identical packets when a tag attached to an object moves along a conveyor belt past an interrogator. The middleware reduces the chatter of the interrogator to a concise and structured stream of unique packets. These packets are then typically sent to an enterprise application that actually processes the data. Examples of such applications include those that perform inventory management, supply chain management and analysis, or purchase and backorder handling.
RFID systems present a number of advantages over other object marking and tracking systems. A radio frequency interrogator may be able to read a tag when it is not in line of sight from the interrogator, when the tag is dirty, or when a container encloses the tag. RFID systems may identify objects at greater distances than optical systems, may store information into read/write tags, may operate unattended, and may read tags hidden from visual inspection for security purposes. These advantages make RFID systems useful for tracking objects. They are being adopted for use in retail stores, airports, warehouses, postal facilities, and many other locations. RFID systems will likely be more widely adopted as the price of tags and interrogators decreases.
As organizations strive to adopt RFID systems for tracking objects, they face challenges imposed by the nature of the objects they handle and the environments in which those objects are processed. Radio frequency signals are reflected, refracted, or absorbed by many building, packaging, or object materials. Moving people, vehicles, weather and ambient electromagnetic radiation can also effect the performance of RFID systems. Compounding the situation is a growing diversity of choices among RFID systems and components with dimensions such as cost, range, and power consumption. An RFID tag may deliver varying performance depending upon its orientation and location upon or within a package, its distance from a reader and the frequency at which it operates. Often companies must purchase and evaluate systems through trial and error, a time-consuming and costly process. Radio frequency design and testing software, RF site surveys and prototype systems can assist the process, but these approaches do not address the problem of complex object materials, changing object materials, and the wide variety of RFID tags available. For instance, when an RFID tag with antenna is placed upon a case containing a variety of objects, the objects may affect the reception of the tag's antenna. Moving the tag to another location on the case can determine whether the tag will successfully receive and respond to an RFID interrogator's signal. A need exists for a system that exhaustively and efficiently tests a wide variety of RFID antenna configurations to determine optimal placement of the antenna or antennas with respect to an RFID interrogator antenna or antennas and an object or objects.
U.S. Pat. No. 6,771,399 discloses a system, method and apparatus for translating a carriage from one position to another position utilizing an injection molded plastic translating system The apparatus differs from this invention in that solves the problem of moving by means of a radio-wave-transparent material, but it does not address the problem of placing antennas with respect to one another and objects within their environment.
U.S. Pat. No. 6,104,291 discloses a method and apparatus for simulating physical fields. The apparatus differs from this invention in that it addresses issues of integrated circuit interface. It simulates high frequency effects for the design of on-chip interconnect structures.
U.S. Pat. No. 5,999,861 discloses a method and apparatus for testing RFID tags. The apparatus differs from this invention in that while it moves RFID tags with respect to an RFID interrogator, it does not find optimal placement of antennas, but simply tests the performance of a number of tags within the same interrogator field.
U.S. Pat. No. 5,929,760 discloses an RFID conveyor antenna system in which tags are moved along a conveyor belt past an RFID interrogator. The method differs from this invention in that it does not does not determine the optimal placement of RFID tag antennas with respect to interrogators or objects.